The hypervirulence of Agrobacterium tumefaciens A281 is encoded in a region of pTiBo542 outside of T-DNA

TLDR

Strain A281 is hypervirulent on several solanaceous plants. The authors employed a binary‑vector strategy, constructing plasmids carrying either the L,L‑succinamopine T‑DNA or the remainder of the Ti plasmid from A281 and testing these constructs with complementary regions from heterologous Ti plasmids. Reconstitution experiments showed that hypervirulence on tobacco could be restored with a bipartite strain containing the L,L‑succinamopine T‑DNA and a separate vir region, that pEHA101 complemented octopine T‑DNA to hypervirulence on tobacco and tomato, and that nopaline T‑DNA was better complemented on tomato by pEHA101 but not to hypervirulence, while L,L‑succinamopine T‑DNA could not be complemented to hypervirulence with heterologous vir regions, indicating that strain A281’s hypervirulence is encoded by non‑T‑DNA sequences on the Ti plasmid.

Abstract

We used a binary-vector strategy to study the hypervirulence of Agrobacterium tumefaciens A281, an L,L-succinamopine strain. Strain A281 is hypervirulent on several solanaceous plants. We constructed plasmids (pCS65 and pCS277) carrying either the transferred DNA (T-DNA) or the remainder of the tumor-inducing (Ti) plasmid (pEHA101) from this strain and tested each of these constructs in trans with complementary regions from heterologous Ti plasmids. Hypervirulence on tobacco could be reconstructed in a bipartite strain with the L,L-succinamopine T-DNA and the vir region on separate plasmids. pEHA101 was able to complement octopine T-DNA to hypervirulence on tobacco and tomato plants. Nopaline T-DNA was complemented better on tomato plants by pEHA101 than it was by its own nopaline vir region, but not to hypervirulence. L,L-Succinamopine T-DNA could not be complemented to hypervirulence on tobacco and tomato plants with either heterologous vir region. From these results we suggest that the hypervirulence of strain A281 is due to non-T-DNA sequences on the Ti plasmid.